[libc][math] Added atanf function.

Performance by core-math (core-math/glibc 2.31/current llvm-14):
28.879/20.843/20.15

Differential Revision: https://reviews.llvm.org/D132842

GitOrigin-RevId: 77e1d9beedeccfc0e368b3f34956e12f78d0faa2
22 files changed